Troschel, in Schomburgk, 1848
Yellow-spotted river turtle
Recognition
The oval, adult carapace (to 46.5 cm) is slightly domed, broadest at the center, and has a smooth posterior rim and a cervical indentation. A medial keel is usually present, pronounced in juveniles but reduced to a low mound on the 2nd and 3rd vertebrals in adults. Vertebrals are broader than long in juveniles, but the 2nd and 3rd may lengthen to become as long or slightly longer than broad in adults. Vertebral 5 is the smallest and it is posteriorly expanded. The posterior marginals are flared over the hindlimbs and tail. Surfaces of the scutes are rough with raised annuli. The carapace of juveniles is brown to greenish gray with a narrow yellow border, that of adults is olive to dark gray or brown. The plastron does not cover the entire carapacial opening. Its large anterior lobe is slightly broader than the posterior lobe, and is rounded in front. The posterior lobe is slightly tapered toward the rear, and there is an anal notch. The bridge is broad but not as wide as the plastral posterior lobe. The plastral formula usually is: pect > abd > fem > intergul > an > gul > hum. The intergular scute is long and narrow; it completely separates the gulars and partially separates the humerals. The yellow plastron and bridge may develop dark blotches with age. The elongated head has a protruding snout and a distinctly notched upper jaw. No interorbital groove is present, and the interorbital breadth is less than the height of the orbit. Two ridges occur on the triturating surface of the upper jaw. Premaxillae are short and do not separate the maxillae or extend backward to the choanal rim. The foramina incisiva occur completely within the premaxillae. A small vomer may be present. The tympanum is broader than the orbit. The interparietal scale is elongated, but does not completely separate the parietals. Small suboculars are usually present. One or two chin barbels are present (Medem, 1964)—one in Orinoco populations, two in Amazonian populations. The head is gray to olive or brown with yellow spots—one on top of the snout, one on each side of the snout extending to the upper jaw rim, another on each side of the head extending from the lower posterior edge of the orbit to the corner of the mouth, and one on each tympanum. Jaws are dark brown or black, but the chin has a transverse yellow bar and a yellow spot on each side below the corner of the mouth. Limbs are gray to olive brown. Usually there are three large scales on the posterior margin of the hind foot.
The karyotype is 2n = 28; 6 large to medium-sized metacentrics and submetacentrics, 4 large to medium-sized subtelocentrics, 14 small to very small metacentrics and submetacentrics, and 4 small acrocentric and subtelocentric chromosomes (Ayres et al., 1969; Rhodin et al., 1978).
Males have longer, thicker tails than do females and retain more of the juvenile head pattern. Females grow larger (to 46.5 cm) than males (to 33.5 cm).
Distribution
This turtle lives in the Caribbean drainages of the Guianas, Venezuela, and Colombia, and the upper tributaries of the Amazon River in Colombia, eastern Ecuador, northeastern Peru, northern Bolivia, southern Venezuela, and Brazil.
Habitat
Podocnemis unifilis lives in lakes, ponds, flood-plain pools, swamps, lagoons, and oxbows along major rivers.
Natural History
Females probably mature at a carapace length of about 30 cm. Artner (in prep.) describes courtship as follows: the male swims around the female, faces her, and then strokes her muzzle with one or both of his forelegs in a way reminiscent of North American sliders and cooters (Trachemys and Pseudemys). Biting of head and neck, as described by Rudloff (1990), and the intercourse itself were not observed by Artner.
In Brazil, the nesting season is in June and July on the Rio Purus, September and October on the Rio Trombetas, and December on the Rio Negro (Vanzolini, 1977). Thorbjarnarson et al. (1993) reported nesting occurs in January and February along the Capanaparo River in Venezuela, whereas in Colombia, the season varies from July to December in the several rivers (Medem, 1964). Along the Rio Pacaya in Peru the nesting season lasts from late June to October, but 90% of the eggs are laid from late July to Early September (Soini, 1994). About 80% of the eggs are laid at night, usually on river banks, but some nestings also take place on the shores of oxbow lakes, ponds, and backwater streams. Nesting is often a gregarious event, with several females excavation in the same area at the same time. Nests are shallow holes (9.5-23.0 cm deep) usually dug in sandy or loamy soils along rivers and streams, but also on floating mats of vegetation and organic matter (Thorbjarnarson and Da Silveira, 1996).
Two or more clutches of 6-52 eggs are laid each season, at intervals of 9-10 days (Soini, 1994, 1996); the average clutch size in over 16,000 nests was 19 eggs (Soares, 1996). Souza and Vogt (1994) determined the pivotal temperature of this species at 32°C under laboratory conditions; incubation temperatures higher than 32°C produced 90-100% females, temperatures of 28-31°C yielded approximately 80% males. Under natural conditions, the substrate plays an important role in determining the sex ratio (Souza and Vogt, 1994). The eggs are ellipsoidal (41-53 x 25-37 mm) with hard calcareous shells. Incubation under semi-natural conditions takes 60-69 days (Thorbjarnarson et al., 1993); Soares (1996) recorded an average incubation period of 73 days. Hatchlings are about 40 mm long and weigh 9-22 g (Pritchard and Trebbau, 1984; Thorbjarnarson et al., 1993; Artner, in prep.).
Podocnemis unifilis is primarily a vegetarian, but captives will eat fish and meat. They sometimes use an inertial feeding mechanism, termed neustophagia, for extraction of fine particulate matter from the water surface.
Remark
Pritchard and Trebbau (1984) and David (1994) have demonstrated that the scientific name Podocnemis unifilis that is used for this species actually is incorrect. Schweigger (1812) described a juvenile as Emys cayennensis, the type of which has been located in Paris (MNHN 8359). As it undoubtedly concerns P. unifilis (Bour, in David, 1994), this species' correct name should be Podocnemis cayennensis (Schweigger, 1812). However, as the name P. unifilis has been used for decades, and the name P. cayennensis also has been applied for the red-headed river turtle Podocnemis erythrocephala, Pritchard and Trebbau (1984) proposed formal action to suppress the name cayennensis.
IUCN Red List Status (1996)
Vulnerable (A1acd).